1. Field of the Invention
This invention relates to apparatus for applying intracavitary radiotherapy.
2. Description of Related Art
Apparatus for this purpose is disclosed in U.S. Pat. No 4,233,517 issued Nov. 11, 1980 to Van't Hooft, which in turn refers to a French Pat. No. 1,593,557. In the type of apparatus described in these patents, radioactive material is conveyed to a desired location within the patient by transporting a chain of balls pneumatically to and from an appropriately inserted applicator, the ball being made up of radioactive balls appropriately spaced by non-radioactive metallic balls. The ball chain is assembled and stored prior to use and sorted after use in a control unit within which the balls are transported pneumatically and sorting is carried out magnetically. This entails that the spacer balls are of magnetic material, in practice steel. The radioactive balls consist of a radioactive filling within a comparatively thin stainless steel shell, and the spacer balls usually substantially outnumber the radioactive balls.
The balls are subjected to a great deal of manipulation both in the control unit and in transit to and from the patient, for example, the ball chain must be returned to the control unit every time a nurse or visitor wishes to enter the room in which the patient is being treated, and every time it is desired to alter the configuration of the ball chain. The massive nature of the spacer balls results in considerable battering of the radioactive balls during such manipulation, with the attendant risk of rupture or leakage, and this severely limits the amount of manipulation which can be tolerated since a ruptured or leaky ball is likely to distribute radioactive material throughout the system entailing a time-consuming, hazardous and very expensive clean-up and rebuilding operation. This problem restricts the possibilities for changing the ball chain configuration during the course of a treatment, and also severely restricts access to the patient by other personnel. Even with appropriate precautions, the risk of ball leakage or rupture still exists. A further disadvantage of the steel spacer balls is that they provide partial shielding of the radioactive balls, requiring compensation when calculating radiation dosage, and that they are radiographically opaque which limits the information which can be obtained from check-film radiography.